The present invention relates to an image pick-up device comprising a fisheye lens, an image display device and an information recording medium, all of which can obtain a high-quality converted image when an image picked up by the fisheye lens is converted into a plane image.
A monitoring system using a camera which enables product examination at a plant or construction work at a construction site to be monitored from a remote place has recently been developed. In this monitoring system, depending on what is monitored, capability of monitoring a wide range at a limited number of cameras is desired. To realize this, the development of a monitoring system comprising a fisheye lens which can pick up an image of all the directions of the field of view around the optical axis at a field angle of at least 90.degree. in each direction with respect to the optical axis is under way.
Use of this fisheye lens makes it possible to obtain an image of all the space with a single camera. That is, the space is regarded as a single sphere, a camera is installed at the center of the sphere, an image of half of the sphere is picked up by the fisheye lens, the camera is turned at an angle of 180.degree. from that position, an image of the other half of the sphere in the opposite direction is picked up, and the two images are combined together to obtain an image of all the directions of the field of view in the space of 360.degree., that is, the sphere. This image is converted into a plane image.
As the monitoring system comprising a fisheye lens of the prior art, there is a system disclosed by Japanese Patent Application Laid-open No. Hei6-501585 (to be referred to as "prior art" hereinafter), for example. Although this prior art makes it possible to pick up an image of all the directions of the field of view, the lens used in the prior art is a fisheye lens having a relationship of h=f.multidot..theta. (wherein h is the height of an image of a subject at a certain point obtained by the fisheye lens, f is the focal distance of the fisheye lens and .theta. is a field angle). This is obvious from the fact that Nikon's 8-mm f/2.8 lens is used as the fisheye lens in the above Japanese Patent Application Laid-open No. Hei6-501585. Conventional fisheye lenses generally have a relationship of h=f.multidot..theta. and Nikon's 8-mm f/2.8 fisheye lens has the above relationship of h=f.multidot..theta..
The method of picking up an image by a fisheye lens having this relationship of h=f.multidot..theta. and converting the image into a plane image is called "equidistant projection". Since an image picked up by a fisheye lens having the above characteristics has a small volume of image data on its peripheral portion (field angle of around 90.degree. with respect to the optical axis of the fisheye lens), when the image is converted into a plane image, there are many missing portions of image data on the peripheral portion of the image and the missing portions must be interpolated. In addition, the image picked up by the fisheye lens having the above characteristics involves such a problem that the peripheral portion of the image is distorted.
An object of the present invention is to provide an image pick-up device comprising a fisheye lens, an image display device and an information recording medium, which minimize missing portions of image data by extracting a large volume of image data at a field angle of around 90.degree. with respect to the optical axis of the fisheye lens to reduce interpolating of the missing portions and can obtain a natural plane image when images of all the directions of the field of view around the optical axis are picked up at a field angle of at least 90.degree. with respect to the optical axis and are converted into plane images.
Various other objects, advantages and features of the present invention will become readily apparent to those of ordinary skill in the art, and the novel features will be particularly pointed out in the appended claims.